Add Background Audio, Update UI

[threethan]

This version allows apps like Discord and Spotify to function almost flawlessly on the Quest 2 (don't have a quest 1 to test)
However, this requires device owner permissions. I'm gonna hold off on uploading my own apk for a few days, since changing forks would require a factory reset. (You can't install updates to admin apps unless signatures match)

• A new option has been added to enable background audio
  When run, this will grab a list of all installed packages
  Every 2 seconds, all packages will be given the "PLAY_AUDIO" and "RECORD_AUDIO" permissions
  These permissions are enabled by default on all android apps,
  but the Quest OS disables them when an app is minimized or the headset is unlocked

  Music and voice chat apps now work on the Quest/2, even when in game
  This does not stop the OS from killing apps in the background, which will still happen when a game is quit
  The enabler service will remain though, so only the audio apps need to be reinitialized

• The user interface has been updated to better match with the Quest v30 default apps
  Colors were taken from screenshots, fonts were changed, and icons were added

• README has been updated to explain the new feature

• README has an updated screenshot

[basti564]

Thank you for your pull request!
This very cool feature, I have just tested it on my devices an it works great.
I will publish a signed version of Oculess with these features soon.

[D3SOX]

Thank you, this works great!

The only thing I noticed is that the OS pauses media playback when an update or unsupported app dialog comes up (For example, with modded Beat Saber).
So you wouldn't be able to use Spotify as background music playback with such apps because you can't resume the playback in a VR app. However, apps that don't make use of Android's media player feature like Discord work fine.

[threethan]

@D3SOX I've noticed this. That seems to be normal android behavior - media playback from one source gets paused when another starts. I incorrectly stated in the PR that apps seem to be suspended when you quit a game - turns out media is only paused. Normally it would be possible to resume playback from the notification shade (the quest seems to use it's own notification implementation instead of android's) or by using a hardware play/pause button (the quest seems to ignore hardware media buttons). However, I managed to resume spotify remotely using spotify connect.

It might be possible to work around this using an accessibility service. (I can confirm that custom accessibility interactions work fine on the quest) This might also make it possible to run at startup, as typical "launch-at-startup" apps don't work on the quest.